MabiPro: The Authentic Old-School Mabinogi Experience

I have my Playing Instrument at 99% at Rank E. No matter how many times I practice or fight with the instrument, it won't let me reach 100% nor give me that option to rank up despite having the AP to do so. Consequently, I can't finish my music quest that requires rank D instrument playing to complete it.

I've tried looking for solutions in general all over google and tried my own ideas, and nothing has worked. Please help, thank you. x.x